Petroleum hydrocarbons, petrochemicals, and their feedstocks are commonly heated to temperatures ranging from 100° F. to about 1000° F. during processing. Similarly, many petroleum hydrocarbons used as heating fluids on the “hot side” of heating and heat exchange systems are also heated to such temperature ranges. When heated to elevated temperatures, petroleum hydrocarbons produce a separate phase known as fouling deposits within the petroleum hydrocarbon. As the name implies, these fouling deposits form deposits on the surfaces of processing and heating equipment, thereby fouling such surfaces. These deposits are of considerable concern in the petroleum hydrocarbon processing and heating industries.
In petroleum hydrocarbon processing, the deposits reduce the rate of heat transfer to the crude oil, and eventually, reduce throughput rates. In some cases, the fouling can even block the flow of crude oil through processing equipment and piping or clog filter screens, valves, and traps. Accordingly, fouling results in increased energy costs, increased maintenance costs for cleaning or screen replacements, and increased capital costs for the modification or replacement of refinery equipment.
The exact mechanism of fouling is not fully understood, however it appears that several different components of crude oil may contribute to fouling. Such components include asphaltenes, coke, organic polymers and organic reaction products, inorganic silicates, inorganic salts, and metal oxides or sulfides. The metal oxides or sulfides may further exacerbate fouling by accelerating the hydrocarbon oxidation rate by promoting degenerative chain branching, resulting in free radicals. The free radicals may initiate oxidation and polymerization reactions which form gum and sediments.